The present invention relates in one aspect to a process for preparing block copolymers by metathesis of two or more polymers containing ethylenic unsaturation and in another aspect to metal-block copolymer compositions derived therefrom. Numerous olefin metathesis processes are previously known in the art. In general, olefin metathesis involves catalytic cleavage of one or more olefins at a point of unsaturation and recombination of the resulting cleavage products to form different olefin containing reaction products. Often, low molecular weight olefins and cyclic olefins are employed as reagents in the foregoing reaction mixtures in order to provide low viscosity reaction mixtures, well defined reaction products, reduced polymer product molecular weight, and/or mixtures suitable for reaction injection molding (RIM) compositions. Examples of the foregoing processes are disclosed in U.S. Pat. Nos. 5,731,383, 4,994,535, 4,049,616, 3,891,816, 3,692,872, and elsewhere.
Metathesis involving polymeric olefins is also known. In Macromol., 33, 1494-1496 (2000), solid polymers were depolymerized by surface contact with a metathesis catalyst. Reaction products of polymer metathesis can include random or block copolymers, functionalized polymers obtained through functionalization of resulting terminal unsaturation, ring opened metathesis products, and even cross-linked solids. Metathesis of two or more different olefins is referred to as a “cross-metathesis”. Examples of such processes are disclosed by U.S. Pat. Nos. 6,867,274, 6,410,110, 5,603,985, 5,559,190, 5,446,102, 4,049,616, and other references. Suitable unsaturated polymers for the foregoing processes include diene homopolymers and copolymers or partially hydrogenated derivatives thereof. Use of cyclic olefins can result in the formation of polymers having narrow molecular weight distributions. For example, preparations of linear polyethylene and poly(ethylidene-norbornene)/polycyclopentene diblock copolymers by ring opening metathesis of polycyclopentene or sequential polymerization of mixtures of ethylidene-norbornene and polycyclopentene were disclosed in Macromol., 33(25), 9215-9221 (2000).
In U.S. Pat. Nos. 3,692,872, 3,891,816 and 4,010,224 graft and block copolymers and interpolymers were prepared by metathesis of two polymers containing olefinic unsaturation, such as polybutadiene or polyisoprene. Monomers such as cyclooctene or dimers such as cyclooctadiene-cyclopentadiene dimer could be included in the polymerization as well. Similar processes involving the cross-metathesis of polybutadiene with polycyclooctene or polycyclododecene as well as grafting of EPDM polymers via metathesis were disclosed in DE 2,131,355 and DE 2,242,794. In the former process, “thermoplastic properties were imparted to the elastomer”. A summary of the work appeared in J. Mol. Catal., 15, 3-19 (1982).
Similarly, in U.S. Pat. Nos. 3,692,872, 3,891,816 and 4,010,224 graft and block copolymers and interpolymers were prepared by metathesis of two polymers containing olefinic unsaturation, such as polybutadiene and polyisoprene. Monomers and dimers such as cyclooctene or cyclooctadiene-cyclopentadiene dimer could be included in the polymerization as well. Exemplified polymer pairs included partially polymerized cements of polycyclooctene and polycyclooctadiene (Ex. I), EPDM/polybutadiene (Ex. II and V), and two EPDM/cyclooctadiene copolymers having differing cyclooctadiene contents (Ex. III).
In Macromol., 36, 9675-96777 (2003) the ethenolysis of polypropylene/1,3-butadiene copolymers to prepare polymers having slightly increased melting temperature for the isotactic polymer segments due to improved packing of shorter chain segments was disclosed. In German Democratic Republic patents DD 146,052 and DD 146,053, 1,4-cis-polybutadiene and copolymers such as ABS rubber or SB rubber were subjected to metathetic depolymerization optionally in the presence of a functionalizing agent, especially an unsaturated carboxylic acid ester. According to U.S. Pat. No. 7,022,789, the products were polydisperse rubbers indicating the presence of cross-linking due to undesirable quantities of vinyl groups in the product.
Disadvantageously, the foregoing known polymeric olefin metathesis products are lacking in desirable physical properties due to the fact that at equilibrium, the individual block lengths, which approach the lengths of the unsaturated segments in the starting polymer reagents, are undesirably short and lacking in polymeric character. Moreover, the individual blocks do not differ significantly from one another in chemical properties. For example, segment properties of polycyclooctene and polycyclododecene or of polybutadiene and polyisoprene, are nearly chemically equivalent. Copolymers comprised of such polymer segments do not possess advantaged properties. Conventional block copolymers, such as those prepared by anionic polymerization techniques readily incorporate dissimilar, immiscible, lengthy segments in the same polymer chain. Because the segments are of sufficient molecular weight to possess measurable physical properties, such as glass transition temperature (Tg), crystalline melting point (Tm), dielectric constant or solubility parameter the resulting polymers possess enhanced properties. For example, the presence of crystalline polymer segments having a relatively high melting point and elastomeric polymer segments within the same polymer chain gives thermoplastic materials having improved elastomeric and mechanical properties, such as high tensile strength, hysteresis, and tear properties.
The previously discussed processes utilized polybutadiene or similar polymers prepared by free radical techniques which possess undesirably high quantities of pendant vinyl groups (instead of terminal or internal unsaturation) due to uncontrolled 1,2-addition of the conjugated diene. This results in undesirably high levels of pendant vinyl functionality in the metathesis products unless extensive hydrogenation of the polymer is employed to first reduce the level of such pendant unsaturation. Polymer hydrogenation however is expensive and can result in loss of terminal unsaturation as well. Moreover, polybutadiene is known to be subject to rapid metathetical degradation and ring formation under metathesis conditions, resulting in formation of low molecular weight by-products of little commercial value.
It would be desirable if there were provided a process for the metathesis of unsaturated polymers that is specifically adapted for the formation of differentiated, commercially valuable meta-block copolymer products, having many of the properties of conventional, non-random block copolymers. It would further be desirable if the resulting polymer products were suitable for use as molding resins, adhesives, sealants, compatibilizers, and impact modifiers. Finally, it would be desirable to provide a process for converting readily available, inexpensive, unsaturated polymers into meta-block copolymers having differentiated, commercially valuable properties.